Look at the nation, that’s a crooked smile braces couldn’t even straighten

This use of “crooked smile” marks a shift in the song from the personal to the societal.

America is a mess that “braces couldn’t even straighten”, on the surface appearing friendly like a smile but really having defects as a society, that go deep enough that a simple remedial intervention (the braces in this case) can’t fix.

The defects Cole addresses are racial discrimination (four centuries and counting) and violence (since the beginning of mankind). And the first one precisely originates from our failure to accept those who are different (those with a ‘crooked smile’), even if in essence we are all equal.